This project supports a Biotechnology Resource devoted to mass spectrometry, serving the needs of investigators with NIH sponsored projects in the Midwest and beyond for quantitative low resolution gas chromatograph-mass spectrometer analyses of biological compounds and drugs in complex tissue samples. Chemical ionization is used extensively for increased specificity. Stable isotope tracer analysis of metabolic pathways is pursued in many studies. A novel isotope ratio monitoring mass spectrometer is under design, which provides a gas chromatograph separation system as input to a combustion oven which passes either pure CO2 or N2 from the combusted effluent into the mass spectrometer. This arrangement should provide greatly increased precision while retaining the speed and separatory power of the gas chromatograph.